Columns limits

Unhke the RDC and Oldshue-Rusnton columns where the specific throughput of the scaled-up version is the same as the pilot column, it is the characteristic of the Scheibel column that the throughput of the scaled-up column is on the order of 3-5 times greater than that acheived on the pilot column. The reason for this is that the restricted geometry of the 0.075 m diameter column limits throughput these restrictions are removed in the scaled-up columns. 

Dean et al. [93] used a high performance liquid chromatographic method for the simultaneous determination of primaquine and carboxyprimaquine in plasma with electrochemical detection. After the addition of the internal standard, plasma was deproteinized by the addition of acetonitrile. Nitrogen-dried supernatants, resuspended in mobile phase were analyzed on a C8 reversed-phase column. Limits of detection for primaquine and carboxyprimaquine were 2 and 5 ng/mL with quantitation limits of 5 and 20 ng/mL, respectively. The assay sensitivity and specificity are sufficient to permit quantitation of the drug in plasma for pharmacokinetics following low dose (30 mg, base) oral administration of primaquine, typically used in the treatment of malaria and P. carinii pneumonia. 

Sample Elements Species Separation process and column Limits of detection Reference... 

Microcapillary (0.200 -s- 0.300 mm diameter) and nanocapiUary (0.075 -t- 0.100 mm diameter) columns limit solvent consumption and interface more easily with mass spectrometer detectors. They can assay only small amounts of sample and are superior for managing Joule heating due to their enhanced surface area to volume ratio and lower volumetric flow rate (uL/min) for a given linear mobile phase velocity (mm/sec). 

In summary, the diol-phase column had better separation resolution for procyanidin oligomers than the silica column. Limits of quantitation in the diol-phase method were significantly lower than those in the silica... 

Singhal and Cohn (S26) used exclusion chromatography with anion-exchange columns for the separation of nucleosides and bases. Brown et al. (B30) optimized this technique and obtained a separation of the naturally occurring free nucleosides and bases in cell extracts. Although these separations were useful, the analysis time of 2 h and relatively low efficiencies of the columns limited their usefulness in routine analyses. 

Most data on short columns Limited data... 

The scale-up of a fixed-bed separation may be carried out by increasing the diameter of a column, the length of the packed bed, and/or the flow rate of the feed solution. The pressure drop through the column limits the length of the packed bed. The amount of adsorbate treated per unit time and the unit sectional area of a column will increase with the linear velocity of the feed. However, the slope of the breakthrough curve becomes gentle with an increase in the velocity, when the intraparticle resistance of solute transfer is dominant, and thus the fraction of the column capacity available at the break point will decrease. Therefore, the linear... 

Although, greater sample capacities are attained with the use of packed columns in supercritical fluid chromatography as in all other forms of chromatography, the pressure drop across the column limits the length and hence the total chromatographic efficiency (total number of the theoretical plates) obtainable. 

SCOT (support coated open tubular) and conventional capillary columns are widely used in GC-MS analysis because of their low carrier gas flow requirements and superior resolution. Much of our GC-MS work, including pesticide analysis, is done with SCOT columns, flow rates being 5-15 ml/minute. All capillary columns limit the injection volume to 2 or 3 microliters or less. 

Quantitation of total polar compounds (TPC) is the basis of legislation in many countries for the control of used frying fats. The method is gravimetric and based on the adsorption of polar compounds onto a silica gel column. Limits up to 27% have been set for TPC in countries where frying oils are regulated. There are approved methods (lUPAC, AOAC) for TPC determinations. TPC can also be determined with Sep-Pak cartridges. An alternative technique uses the latroscan thin-layer chromatography/flame ionization system (Sebedio et al., 1987). 

The majority of reports in the literature concerning SEC of peptides and proteins tend to describe chromatographic conditions designed to ensure a pure size exclusion process, although it is often overlooked that the nonideal properties of size exclusion columns can be advantageous in the separation of peptides [37,77]. Excellent examples of this were reported by Yasukawa et al. [78], who separated various hydrophilic and hydrophobic dipeptides on a non-silica-based column by isocratic elution with 50 mM sodium phosphate buffer (pH 7.0). The peptides, retained by adsorption, were eluted in the order of increasing hydrophobicity. Similarly, Mant et al. [37] demonstrated that the separation of five peptide standards of 10, 20, 30, 40, and 50 residues was markedly improved on a SynChropak GPC-60 column when advantage was taken of the nonspecific adsorptive properties of the column rather than when the column was utilized under conditions of ideal SEC. Thus, what is occasionally viewed as a column limitation may become a useful analytical tool. 

BSUs limit Columns limit = sudden change of properties ... 

Inoperable Ball Column Limit 1 6 Total Control Considerations 1 7 Speed of Control Considerations... 

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